Cute tablets for kids: That's the deceptively simple concept behind the Nabi, the high-tech toy that's made Fuhu Inc.'s fastest-growing company two years in a row. But it couldn't take on its big-name tablet competitors on that slogan alone. Here are three ingredients in its recipe for success:

1. One for every age. There are Nabis for toddlers ($100), kids ($180), and tweens ($250 to $290)--meaning that children who outgrow their first tablets will be clamoring for their parents to buy the more advanced versions. Bigger Nabis, with 20-inch and 24-inch screens, are due out this fall. Every Nabi comes with parental controls, including browser blocks on nonapproved websites and curfews that shut the devices off.

2. Special Additions. Dora the Explorer will help your child learn the alphabet--if you splurge on the Nick Jr. Nabi 2 ($140). Fuhu sells other special-edition tablets from Nickelodeon ($200, only at Walmart), Disney ($199, only at Best Buy), and DreamWorks ($270). That DreamTab comes with a high-end processor and custom content, including an app that teaches kids how to draw characters such as Shrek.

3. Accessory Overload. Want to personalize your kid's Nabi? Fuhu will sell you silicone decals ($13 for five sports logos; $25 for an alphabet set) or a glow-in-the-dark soft cover ($30), along with one of its bright-red Nabi-carrying backpacks ($50) and car-charging kits ($40). They may seem frivolous, but these sorts of add-ons made up about 25 percent of Fuhu's sales last year, up from about 10 percent in 2012.

Two-Time Chart Topper

Before this year, only one company had landed at the top of the Inc. 500 two years in a row. Now Fuhu has pulled off that feat, after blowing past the three-year sales growth that made it our No. 1 company in 2013. Last year, the tablet maker reported a whopping 158,956.9 percent increase in revenue from 2010. Fuhu did that by expanding pretty much everything it could. At left, its growth by the numbers.